The invention relates generally to network communications. More specifically, the invention relates to systems and methods that provide a shared mesh restoration with pre-configured, standby lightpaths for restoring services in all-optical reconfigurable network architectures after experiencing a network failure.
Ultra Long Haul (ULH) technologies for Dense Wavelength Division Multiplexing (DWDM) transports are being deployed due to their high-capacity and capital savings. A first-generation ULH network typically includes a set of point-to-point linear systems with each linear system having two terminals. Between the two terminals, there may be one or more Reconfigurable Optical Add-Drop Multiplexers (ROADMs), where traffic may be added or dropped, or expressed through optically by degree-2 ROADMs.
Using these ULH systems, a wavelength connection or lightpath is able to travel a long distance such as 1500 km or more without requiring optical to electronic to optical (OEO) regeneration. This distance limit is referred to as the ULH-reach. An OEO regenerator is needed when a connection length is longer than the ULH-reach. When a connection has to travel through two linear ULH systems, an OEO regenerator is also needed even if its length is within its ULH-reach. Since the OEO regenerators are expensive devices, first generation ULH networks were not inexpensive. They also complicate dynamic reconfiguration and restoration in the Optical Layer (OL).
To reduce the cost of OEO regeneration and enable automatic re-configurability and dynamic restoration via wavelength switching and tuning, next generation optical networks are moving toward an all-optical mesh network. These configurations convert the terminals and degree-2 ROADMs to higher-degree ROADMs to switch and route wavelengths optically, which is known as Photonic Cross Connect (PXC).
FIG. 1 shows a next generation core IP over ROADM over fiber network architecture. The IP network is the overlay network that is transported over the ROADM-based OL network. All of the middle SONET and Digital Cross-Connect System (DCS) layers are eliminated. Traditional sub-wavelength Time Division Multiplexing (TDM) private line service may be transported over the IP network via pseudo-wire circuit emulation with guaranteed minimum latency and quality of service (QoS). Besides providing direct links for the IP layer, the optical network also provides wavelength services via optical connections that comprise one or more wavelengths.
Traffic originates from a source point S to a destination point D and is routed through the network over a series of links. Once traffic is received into its network at the source point S, the network has to route the traffic over a number of different links (the Layer 1 transport network) to have it arrive at the destination point D. Each link segment that the network uses has two ends. Each end of the link segment typically has a router that can detect if traffic is flowing. An inventory of how the traffic flows from source S to destination D lists all the link segments involved. If one of the links fails and the traffic stops flowing, an alarm is sent to a network maintenance (surveillance) system.
Today, large IP backbone networks are deployed directly over sequences of point-to-point Wavelength Division Multiplexing (WDM), Dense WDM (DWDM) systems, or chains of newer ROADM-based ULH systems interconnected by OEO regenerators.
Both IP and wavelength services have stringent quality requirements for their high priority traffic. One requirement is resiliency against network failures that includes performing a sub-second restoration for high priority traffic that has experienced a single link/node failure, and for a small percentage of mission critical traffic, the ability to restore after experiencing multiple link/node failures.
In an all-optical ULH network, dynamically establishing a new restoration connection from scratch involves not only tuning lasers and receivers to the appropriate frequencies and cross connecting the ROADMs/PXCs, but alSo triggering several feedback loop segments that are responsible for power equalization. This is necessary because the new restoration wavelength(s) change the power profile on each link along the restoration path. The whole process can be slow and often unacceptable to large carriers. Unlike opaque optical networks, where OEO conversions occur in the signal path at either the WDM systems if transponders (that incorporate a transmitter and receiver) are present, or switches if transceivers are present, a transparent, all-optical ULH network does not have OEO conversion/regeneration in the signal path and may require OEO regenerators for some nodes.
Optimal regenerator placement becomes a critical problem in all-optical ULH network design. Because of the differences between opaque and transparent optical networks, shared mesh restoration schemes for opaque optical networks cannot be applied to transparent optical ULH networks.
Shared mesh restoration has been used in opaque optical networks where all restoration channels on each link are pre-reserved and each node has wavelength conversion capability. When a failure is detected, a pre-planned restoration path will be dynamically established by cross-connecting any available channel on each link along the pre-planned restoration path. There is no wavelength assignment involved. Previous shared mesh restoration schemes only consider single network failure scenarios.
The challenge in reliable optical network design is to provide fast restoration in conjunction with restoration capacity in a cost effective manner.
What is desired is a sub-second restoration system and method for optical networks that maximizes sharing among single, and multiple network failures to minimize overall network restoration capacity requirements.